Get them direct through Sandisk online stores in the US or UK, exclusive to them at present. If, like me, you don't live in the US use Shipito to have it sent to you. They are costly at present $199US...

I,ve had 2 32gb and 2 16gb cards turn out to be fake in my quest to get a good but reasonably priced working one - I don,t even bother putting them in my phone any more , simply connect them to your pc in a card reader of some kind and run h2testw (free download) this will perform read/write tests and tell you if the card is fake/defective or ok